Different Forms Of Sulfur Content And δ³⁴S In Topsoils And The Comparative Study With Mosses

Soil is an important media to contact atmosphere, lithosphere,hydrosphere and biosphere, and its primary function is supporting crop growth by supplying water, sulfur and some other nutrition constituents. Soil is also the main supporter to provide plants sulfur and the sulfur conditions in soil can directly effect their growth and survival. In order to explore soil sulfur contents, isotope values and the possible sources, we collected forest topsoils and epilithic mosses in six provinces including Jiangxi, Zhejiang, Yunnan, Guizhou, Fujian and Hebei. Then the contents and δ34S of total sulfur, water-soluble sulfur, absorbed sulfur and oganic sulfur were determined. We have analysed concentration characteristics of different soil sulfur patterns in different places and evaluated the soil sulfur conditions by the standard of the contents of available sulfur(water-soluble sulfur and absorbed sulfur). And the contents of soil total carbon and nitrogen and their relationships with total sulfur were determined at the same time. The δ4S of rainwater and the soil sulfur contents were used to compare with the δ34S of soil sulfur. Finally, the comparative analysis were conduced between soil sulfur contents and δ34S with mosses to discriminate the possible sources of topsoil sulfur in forest.1.The characteristics and assessments of soil sulfur contentsThe soil total sulfur contents were at the range of0.013%-0.286%, and there are obvious positive correlations between total sulfur and carbon (y=0.7155+24.3959x, R=0.66, p<0.0001), total sulfur and nitrogen (y=0.2358+1.4389x, R=0.59, p<0.0001).Oganic sulfur is the main soil sulfur pattern taking over52%～91%.The percentage of water-soluble sulfur were very low, only1.4%～10.3%. The contents of absorbed sulfur is more than water-soluble sulfur but less than oganic sulfur, the lowest percentage is7.86%, in Mount Lu, and the highest is47.7%, in Anyi where absorbed sulfur is the main soil sulfur pattern.The obtained contents of available sulfur were generally high,64.4mg/kg～362.6mg/kg. If taking the standard of Liu Chongqun available sulfur, our results were much higher than25mg/kg. which means the soils were not lack or potential lack of sulfur.If taking total sulfur,150mg/kg as the standard, only one sample, in Fuyuan of Yunnan Province is less than that, and sulfur was not able to run off from our samples easily.2.The834S characteristics of soil sulfursThe834S of topsoil total sulfur were generally positive and the ranges of water-soluble and absorbed sulfur were-6.287‰～+9.948‰and-6.555‰～+8.689‰, respectively which were lower than the δ34S of total sulfur and the obvious linear relationship existed between them, y=-0.0557+1.0002x, R=0.9931, p<0.0001.That means isotopic fractionation does not happen in the process of SO42-adsorption and desadsorption. The834S of oganic sulfur were the highest. The δ34S of soil SO42-were close to the rainwater, which means soil SO42-possible mainly come from atmospheric deposition, especially rainwater.Except the relationship among water-soluble sulfur contents, absorbed sulfur contents and organic sulfur contents, absorbed sulfur content with the δ34S of oganic sulfur, the organic sulfur content with the δ34S of total sulfur, water-soluble sulfur and absorbed sulfur, the rest of contents and δ34S values had the linear relationship to varying degrees.3.The comparision between soils and mosses in sulfur contents and δ34S values and possible sources of soil sulfursThe soil sulfur contents were all much lower than moss sulfur contents, and if mosses had very high sulfur contents did not mean the soils with high sulfur contents.The weak linear ralationship existed between soil sulfur contents and the density of atmopgeric SO2, on the one hand, for the reason that our samples were collected in the forests away from the urbans, and the effects exerted by the industry SO2were alleviated.For the other hand, geogenic reasons, like soil partants. soil types, were needed to do furthur analysis.The S/N of mosses, except Guixi.0.316±0.181. the rest were less than0.15with the range of0.091to0.124and for soils it was between0.11and0.24. And there was no relationship between soils and mosses.The δ34S values of mosses were close to soil SO42-. Except oganic sulfur, the δ34S values of total sulfur, water-soluble sulfur, absorbed sulfur all increased as the δ34S values of mosses increasing, and this means soil sulfur were effected by atmospheric sulfur. Further more, the linear relationship were more obvious between soil the values of SO42-and mosses which proved that soil SO42-mainly come from atmospheric deposition again.The δ34S values of soils in Jiangxi Province were effected by atmospheric sulfur deposition, underground strata, diagenesis, dissolved of gypsum, slurry of animals and the conditions in the process of sample collecting and handling. According to the different sources of atmospheric sulfur, we divided Jiangxi soils into three types. The first, Fengcheng. its soil sulfurs were effected by the local coals, biogenic sulfur and the transported sulfur from northern provinces. The second, Jingdezhen, its soil sulfurs were effected by northern coals, biogenic sulfur and the transported sulfur from northern provinces. The last type includes Gaoan, Qianhu, Mount Lu, Chongren, Yingtan. Dexing and Anyi. their soil sulfurs were effected by local and imported coals, biogenic sulfur and the transported sulfur from northern provinces.